Abstract <p>The influence of treatment with a low-energy high-current electron beam with an electron-beam energy density of 30 J/cm² and a pulse duration of 50 µs on the formation of the surface relief of molybdenum high-speed steel subjected to prior high-temperature tempering was studied. Scanning electron microscopy showed that the surface relief consists of craters ranging from 5 to 250 µm. The average crater size is 91.3 ± 63.1 µm, and the most probable size lies between 40 and 50 µm. A comparative analysis of crater-formation mechanisms based on the concepts of Rayleigh–Taylor, Richtmyer–Meshkov, and thermocapillary instabilities at the melt–plasma interface was performed. It was shown that considering these instabilities separately does not provide an adequate explanation for the formation of craters within this size range. Analysis of the initial stage of combined thermal and concentration-capillary instability together with Rayleigh–Taylor instability, taking into account vapor recoil pressure, made it possible to determine a three-mode dependence of the growth rate of perturbations at the melt–plasma interface on wavelength. The first maximum, caused by the concentration gradient, corresponds to a wavelength of 4.4 µm. The other two maxima correspond to wavelengths of 12.7 and 191.8 µm and arise from the temperature gradient, melt acceleration, and vapor recoil pressure.</p>